BODY PART EXPLAINED The Rotator Cuff
posted on 19/06/2015 1:10:00 AM
BODY PART EXPLAINED The Rotator Cuff
BY: Dr. Matthew Davidson B.Sc., M.Chiro.Director, Hope Island Chiropractic Centre Certified Active Release Technique Provider Member, Chiropractic Association of Australia Member, Sports Chiropractic Australia
DAMAGE TO THE ROTATOR CUFF MUSCLE GROUP IS ONE OF THE MOST COMMON CAUSES OF SHOULDER PAIN. WHETHER YOU’RE A THROWING ATHLETE, SWIMMER, WEIGHT TRAINER, PHYSICAL THERAPIST OR EVEN OFFICE WORKER, ROTATOR CUFF INJURIES ARE OCCURRING MORE FREQUENTLY. A NORMAL FUNCTIONING SHOULDER IS ESSENTIAL FOR MANY TASKS INSIDE AND OUT OF THE SPORTING WORLD. SIGNIFICANT IMPAIRMENT OF THIS MOBILE AND HIGHLY FUNCTIONING JOINT CAN IMPEDE GREATLY ON THE ACTIVITIES OF DAILY LIVING.
The rotator cuff is a dynamic stabiliser of the humeral head by way of forcecouple relationship. By this we mean if one pulls in a certain direction, the other counterbalances it.
Four muscles: the supraspinatus, infraspinatus, teres minor and subscapularis make up the rotator cuff. These muscles are considered to be part of a “cuff” because the inserting tendons of each muscle blend or mould with and reinforce the glenohumeral capsule of the shoulder.
Nerve supply for the supraspinatus and infraspinatus is by the suprascapular nerve. The teres minor is supplied by the axillary nerve; the subscapularis the upper and lower subscapular nerves.1
The rotator cuff is a humeral head depressor (subscapularis, infraspinatus, and teres minor contributing). It balances shearing forces that are applied by larger primemoving muscles such as the deltoid and pectoralis major. The role of the supraspinatus primarily is to compress the humeral head, not depress it.2
When rotator cuff function is impaired the corresponding normal fulcrum of the humeral head is lost, causing an upward displacement and impingement of the subacromial structures and humeral head against the under surface of the acromion. A fulcrum is best described as the point or support on which a lever pivots.3
The function of the supraspinatus is to act primarily as a stabilising compressor of the glenohumeral joint. It therefore creates a fulcrum for the deltoid to act much more efficiently. At the start of arm abduction from a neutral position, the supraspinatus is more important than the deltoid. The medial portion of the deltoid is of greater importance when the arm is elevated at higher angles such as 60°.
Infraspinatus and Teres Minor:
These muscles act as external rotators with the posterior deltoid. According to Kronberg et al, the infraspinatus is more active than the supraspinatus muscle from 120° to 150° abduction.4 This explains why the infraspinatus is affected in prolonged overhead activities.2 The infraspinatus and teres minor muscles also act as dynamic stabilisers, compressing and depressing the shoulder joint. This creates a fulcrum of the deltoid during elevation of the arm that limits anterior and posterior shoulder translation.2
Its function is to act as a dynamic internal rotator. It also contracts eccentrically to protect the shoulder during external rotation. EMG studies have shown more contraction in the subscapularis than the concentrically contracting infraspinatus.2 The subscapularis also acts to passively stabilise excessive anterior translation during external rotation below 90°. This is done through the depressor effects of its lower fibres.4
See Men’s Muscle & Health Sept/Oct 2014 issue Shoulder Impingement by Stent Card (MPhty., BExSc). Page 43 of issue five contains excellent tips on performing effective rotator cuff strengthening exercises. A range of pull, push, external and internal rotation exercises are excellently demonstrated. Your physiotherapist or sports chiropractor may also introduce functional exercises and training tools using bands, tubing or cables. These exercises can mimic movements done in the workplace and everyday activities such as starting a lawn mower or putting a seat belt on in the car. Exercises in scapular setting can also be given to “wake up” the deep stabilisers of the shoulder girdle (serratus anterior and lower trapezius).
What Can Go Wrong: Interesting Facts about Rotator Cuff Tears
The causes of rotator cuff tears are varied, and likely a combination of age-related degenerative change and micro- or macro-trauma. Smoking, high cholesterol and family history have also shown to predispose individuals to tearing.5 Rotator cuff disruption may be characterised as partial or full thickness, acute or chronic, and traumatic or degenerative. No two rotator cuff tears are the same.6
Partial tears close to the bursa (a fluid-filled sac reducing friction located high in the anterior shoulder) are frequently associated with impingement syndrome, and tears closer to the joint surface may be associated with underlying shoulder instability.6 Partial tears present as fraying without complete disruption of the tendon.
Full thickness tears are present in approximately 25 per cent of individuals in their 60s and 50 per cent of individuals in their 80s. Asymptomatic full thickness tears are common and increase with age. 50 per cent of asymptomatic full thickness tears develop symptoms in approx 2-3 years and 50 per cent of those developing symptoms progress in tear size.5 Symptomatic full thickness tears progress in tear size in 50 per cent of cases at an average of two years. Tear size progression correlates with increasing symptoms.
Partial thickness symptomaticand asymptomatic tears progressin tear size slower than fullthickness tears. Tear progression isassociated with worsening pain.5
According to Dr. Robert Tashjian MD, initial non-operative treatment shoulder be considered in all patients with tendinitis, partial thickness tears, small (<1-1.5cm) full thickness tears, all chronic tears in an older age group (>65 years) and all large tears with chronic, irreversible muscle changes.5 A different approach to conservative treatment is through Active Release Techniques®. ART® considers unique restrictions that occur in each shoulder injury, as well as the impact those injuries have on other soft tissue structures along the entire kinetic chain of the
shoulder. Evaluation of the entire rotator cuff must be assessed for relative translation and, if restricted, that muscle must be released in order to restore optimal biomechanics to the shoulder joint.7
Rehabilitation should be gradual, beginning with isometrics and gradually progressing through a strengthening program.
Full thickness tears are surgically repaired by an orthopaedic surgeon, particularly in younger and more active individuals. Sporting athletes are certainly amongst this group and outcomes are usually good for appropriately selected patients. However, high quality evidence-based research is lacking to conclude what surgical treatments are superior or appropriate for a given patient.8
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